The Effect of Oxygen and Hydroxide Ion on Electrochemical Leaching Behavior of Tin

Abstract

The dissolution of tin from waste Pb-free solder was electrochemically investigated in NaOH solution. Two oxidation peaks were observed in a cyclic voltammetry test in 1 kmol m⁻³ NaOH solution at less than 45°C, and the peaks indicate the oxidation of tin to Sn²⁺ and Sn²⁺ to Sn⁴⁺, whereas only one peak was observed at 75°C resulting from the direct oxidation of tin to Sn⁴⁺. The increase in NaOH concentration and the introduction of oxygen enhanced the dissolution of tin in NaOH solution with less than 0.5 kmol m⁻³ whereas that of tin decreased with increasing NaOH concentration further to 1.5 kmol m⁻³ and the decrease in the dissolution of tin was accelerated by introducing oxygen. An optimum waste solder alkaline electrolysis process was found to be at more than 75°C and around 0.5 kmol m⁻³ NaOH based on the cyclic voltammetry and constant current experiment.